Chair having tiltable seat back

Abstract

A chair is provided which comprises a support, a seat arranged above the support, and a seat back tiltably connected to the support behind the seat. The seat back has an upper back supporting portion and a lower waist supporting portion. The chair further comprises a mechanism for deforming the waist supporting portion forward until the seat back tilts rearward to a predetermined intermediate tilt angle but for retarding or stopping such forward deformation when the seat back tilts rearward beyond this intermediate tilt angle. The seat may be made to move rearward as the seat back tilts rearward.

We claim: 
     
       1. A chair comprising: a support structure;   a seat supported on the support structure;   a seat back located behind the seat for tilting rearward against elastic means, the seat back having an upper back supporting portion, the seat back further having a lower waist supporting portion which is elastically deformable forward relative to the back supporting portion; and   control means held in pressing contact with the waist supporting portion of the seat back from behind, the control means being pivotally connected to the support structure to be tiltable rearward;   wherein the chair further comprises means for preventing the control means from tilting rearward until the seat back tilts rearward up to a predetermined intermediate inclination angle but for allowing the control means to tilt rearward when the seat back tilts rearward beyond the predetermined intermediate inclination angle.   
     
     
       2. The chair according to claim 1, wherein the waist supporting portion of the seat back is concave to be offset rearwardly from the back supporting portion before the seat back tilts rearward, the control means presses the waist supporting portion forward to straighten it when the seat back tilts rearward. 
     
     
       3. A chair comprising: a support structure;   a seat supported on the support structure; and   a seat back located behind the seat for tilting rearward against elastic means;   wherein the chair further comprises means for causing the seat to move rearward in response to rearward tilting of the seat back;   wherein the seat back comprises an upper back supporting portion which is substantially non-deformable, the seat back further comprising a lower waist supporting portion which is elastically deformable, the chair further comprising control means for pressing the waist supporting portion of the seat back forward when the seat back tilts rearward; and   wherein the waist supporting portion of the seat back is concave to be offset rearwardly from the back supporting portion before the seat back tilts rearward, the control means pressing the waist supporting portion forward to straighten it when the seat back tilts rearward.   
     
     
       4. The chair according to claim 3, wherein the seat back comprises a downwardly open shell which includes an inner shell plate and an outer shell plate joined to the inner shell plate, the control means extending into the shell from below for pressing contact with the waist supporting portion. 
     
     
       5. A chair comprising: a support structure;   a seat supported on the support structure;   a seat back located behind the seat for tilting rearward against elastic means, the seat back having an upper back supporting portion, the seat back further having a lower waist supporting portion which is elastically deformable forward relative to the back supporting portion; and   control means held in pressing contact with the waist supporting portion of the seat back from behind;   wherein the chair further comprises means for causing the control means to deform the waist supporting portion of the seat back forward relative to the back supporting portion when the seat back tilts rearward at least up to a predetermined intermediate inclination angle but for restraining forward deformation of the waist supporting portion when the seat back tilts rearward beyond the predetermined intermediate inclination angle; and   wherein the waist supporting portion of the seat back is concave to be offset rearwardly from the back supporting portion before the seat back tilts rearward, the control means presses the waist supporting portion forward to straighten it when the seat back tilts rearward.   
     
     
       6. The chair according to claim 5, wherein the waist supporting portion of the seat back is forwardly concave to retreat rearward from the back supporting portion before the seat back tilts rearward, the control means extending along the waist supporting portion and having an upper end provided with at least one pressing roller in contact with the waist supporting portion from behind, the waist supporting portion being provided with at least one regulating roller for contact with the control means to prevent the waist supporting portion from excessively deforming forward relative to the back supporting portion, the waist supporting portion further being provided with at least one cam bulge for contact with the pressing roller, whereby the waist supporting portion of the seat back quickly deforms forward relative to the back supporting portion until the seat back tilts rearward up to the predetermined intermediate inclination angle, whereas forward deformation of the waist supporting portion is at least retarded when the seat back tilts rearward beyond the predetermined intermediate inclination angle. 
     
     
       7. The chair according to claim 5, further comprising means for causing the seat to move rearward in response to rearward tilting of the seat back. 
     
     
       8. The chair according to claim 5, wherein the control means is a control plate fixed to the support structure. 
     
     
       9. A chair comprising: a support structure;   a seat supported on the support structure;   a seat back located behind the seat for tilting rearward against elastic means, the seat back having an upper back supporting portion, the seat back further having a lower waist supporting portion which is elastically deformable forward relative to the back supporting portion; and   control means held in pressing contact with the waist supporting portion of the seat back from behind;   wherein the chair further comprises means for causing the control means to deform the waist supporting portion of the seat back forward relative to the back supporting portion by a greater amount at widthwise outer positions of the waist supporting portion than at a widthwise center position when the seat back tilts rearward.   
     
     
       10. The chair according to claim 9, wherein the waist supporting portion of the seat back has a central section and a pair of side sections separate from the central section, the central section is provided with a rearwardly directed cam bulge having a smaller height, each of the side sections being provided with a rearwardly directed cam bulge having a larger height, the control means obliquely extending rearwardly upward for pressing contact with the respective cam bulges, each of the central and side sections being provided with distance regulating means for preventing excessive forward deformation of the respective sections. 
     
     
       11. The chair according to claim 10, wherein the distance regulating means is a regulating roller. 
     
     
       12. A chair comprising: a support structure;   a seat supported on the support structure;   a seat back located behind the seat for tilting rearward against elastic means, the seat back having an upper back supporting portion, the seat back further having a lower waist supporting portion which is elastically deformable forward relative to the back supporting portion; and   control means held in pressing contact with the waist supporting portion of the seat back from behind, the control means being tiltable rearward;   wherein the chair further comprises means for preventing the control means from tilting rearward until the seat back tilts rearward up to a predetermined intermediate inclination angle but for allowing the control means to tilt rearward when the seat back tilts rearward beyond the predetermined intermediate inclination angle; and   wherein the waist supporting portion of the seat back is concave to be offset rearwardly from the back supporting portion before the seat back tilts rearward, the control means presses the waist supporting portion forward to straighten it when the seat back tilts rearward.   
     
     
       13. A chair comprising: a support structure;   a seat supported on the support structure;   a seat back located behind the seat for tilting rearward against elastic means, the seat back having an upper back supporting portion, the seat back further having a lower waist supporting portion which is elastically deformable forward relative to the back supporting portion; and   control means held in pressing contact with the waist supporting portion of the seat back from behind;   wherein the chair further comprises means for causing the control means to deform the waist supporting portion of the seat back forward relative to the back supporting portion when the seat back tilts rearward at least up to a predetermined intermediate inclination angle but for restraining forward deformation of the waist supporting portion when the seat back tilts rearward beyond the predetermined intermediate inclination angle; and   wherein the waist supporting portion of the seat back is concave to be offset rearwardly from the back supporting portion before the seat back tilts rearward, the control means extending along the waist supporting portion and having an upper end provided with at least one pressing roller in contact with the waist supporting portion from behind, the waist supporting portion being provided with at least one regulating roller for contact with the control means to prevent the waist supporting portion from excessively deforming forward relative to the back supporting portion, the waist supporting portion further being provided with at least one cam bulge for contact with the pressing roller, whereby the waist supporting portion of the seat back quickly deforms forward relative to the back supporting portion until the seat back tilts rearward up to the predetermined intermediate inclination angle, whereas forward deformation of the waist supporting portion is at least retarded when the seat back tilts rearward beyond the predetermined intermediate inclination angle.